py: Remove BITS_PER_WORD definition.

It's only used in one location, to test if << or >> will overflow when
shifting mp_uint_t.  For such a test it's clearer to use sizeof(lhs_val),
which will be valid even if the type of lhs_val changes.

Signed-off-by: Damien George <damien@micropython.org>

py/mpconfig.h

@@ -1538,7 +1538,6 @@ typedef double mp_float_t;
 #ifndef BITS_PER_BYTE
 #define BITS_PER_BYTE (8)
 #endif
-#define BITS_PER_WORD (BITS_PER_BYTE * BYTES_PER_WORD)
 // mp_int_t value with most significant bit set
 #define WORD_MSBIT_HIGH (((mp_uint_t)1) << (BYTES_PER_WORD * 8 - 1))
 

py/runtime.c

@@ -387,7 +387,9 @@ mp_obj_t mp_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
                     if (rhs_val < 0) {
                         // negative shift not allowed
                         mp_raise_ValueError(MP_ERROR_TEXT("negative shift count"));
-                    } else if (rhs_val >= (mp_int_t)BITS_PER_WORD || lhs_val > (MP_SMALL_INT_MAX >> rhs_val) || lhs_val < (MP_SMALL_INT_MIN >> rhs_val)) {
+                    } else if (rhs_val >= (mp_int_t)(sizeof(lhs_val) * BITS_PER_BYTE)
+                               || lhs_val > (MP_SMALL_INT_MAX >> rhs_val)
+                               || lhs_val < (MP_SMALL_INT_MIN >> rhs_val)) {
                         // left-shift will overflow, so use higher precision integer
                         lhs = mp_obj_new_int_from_ll(lhs_val);
                         goto generic_binary_op;
@@ -404,10 +406,10 @@ mp_obj_t mp_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
                         mp_raise_ValueError(MP_ERROR_TEXT("negative shift count"));
                     } else {
                         // standard precision is enough for right-shift
-                        if (rhs_val >= (mp_int_t)BITS_PER_WORD) {
+                        if (rhs_val >= (mp_int_t)(sizeof(lhs_val) * BITS_PER_BYTE)) {
                             // Shifting to big amounts is underfined behavior
                             // in C and is CPU-dependent; propagate sign bit.
-                            rhs_val = BITS_PER_WORD - 1;
+                            rhs_val = sizeof(lhs_val) * BITS_PER_BYTE - 1;
                         }
                         lhs_val >>= rhs_val;
                     }